A two-component developer for a dry processable copying machine, as is well-known, comprises two components, viz., a finely divided toner and a carrier which is larger than the toner in particle size. When mixed and agitated, both components are statically electrified by rubbing, and charges are gained which are opposite in sign to each other. The thus electrified toner is made to adhere electrostatically to an electrostatic latent image formed on a photoreceptor, resulting in the formation of a visible image. This visible image is then transferred and fixed onto a transfer sheet, thus achieving duplication.
In the process as described above, oxidized or unoxidized iron powder has generally been used as the carrier. However, a carrier of this kind has defects, viz., the triboelectrification characteristics thereof is not satisfactory with respect to the toner, and what is worse, it changes with the lapse of time since strong adhesion of the toner to the carrier surface occurs with repeated use and forms a toner film thereon, resulting in the shortening of the developer's life span (so-called spent phenomenon). In addition, there is a large difference in electrification characteristics between carrier in a dry and in a humid atmosphere. More specifically, there exists such a problem that even if carriers exhibit excellent characteristics in Japan, they cannot display their abilities to the fullest in high temperature-high humidity places (e.g., Southeast Asia) whereto they have been exported.
With the intention of obviating the above-described defects, it has been proposed to coat on carrier surface a resin having low surface energy, such as a fluorine-containing resin or a silicone resin, (e.g., in Japanese Patent Kokai Nos. 54-21730 and 58-40557 (The term "Japanese Patent Kokai" as used herein means as "unexamined published Japanese patent application"), Japanese Patent Kokoku Nos. 59-131944 and 59-26945 (The term "Japanese Patent Kokoku" as used herein means an "examined Japanese patent publication"), etc.).
In particular, silicone resins can have various molecular structures depending on the constituent monomers selected for their synthesis, so they not only can be used for the production of carriers which have a wide variety of charge acceptance levels, but they also have many advantages from the working point of view, e.g., that they can be dissolved in various solvents, uniformly coated on the carrier surface with ease, set at relatively low temperatures, and so on.
On the other hand, silicone resins have a defect in that their mechanical strength is generally low, so they come off due to abrasion and generate cracks due to peeling-off after long hours of use, which results in a loss of their excellent characteristics, and a corresponding lowering of copying ability. Thus, silicone resins are not satisfactory with respect to lifespan upon long-term use.
One of the two components which constitute a developer, as the toner is consumed, new toner is supplied in a supplemental amount. On the other hand, a carrier is used continuously. However, it is impossible to restore a carrier's ability which has deteriorated due to continuous use. Therefore, the developer as a whole must be renewed when the carrier has undergone deterioration.
In recent years, requirements for carriers have become more stringent due to popularization of high-speed copying machines and the number of copies needed becomes larger and larger. Therefore, a treatment with conventional silicone resins cannot cope with the present situation.
In addition, the renewal of developer is disadvantageous in cost, as well as being bothersome. Under these circumstances, it was an objective to develop novel carrier-treating agents in high durability.